Means for and method of amplifying electric impulses



Jan. 13, 1931.

A. A. THOMAS MEANS FOR AND METHOD OF AMPLIFYING ELECTRIC IMPULSES FiledJune 18) 1927 5 INVENTOR tronic tube with a cold cathode.

Patented Jan. 13, 1931 PATENT OFFICE-- UNITED STATES ADoLrH A. THOMAS,on NEW YORK, N. Y.

MEANS FOR AND METHOD OF AMPLIFYING ELECTRIC IMPULSES Application filedJune 18,

vacuum tube of novel construction and improved operation. The essentialfeature of my invention is a vacuum tube free from a filament or otherform of electrode to be heated, and this tube is adapted to operate coldfor producing electron discharges, thereby obviating many difiicultiesand objections inherent in the old hot-filament tubes. In other words, Iproduce and utilize an elec- It is generally admitted that the greatesttrouble with the detector and amplifier tubes of the prior art lies inthe filament, which has to be heated I to emit electrons. The filamentrequires a separate source of direct current, popularly known as the Abattery. Attempts have been made to provide a substitutefor the filamentbattery by so-called eliminators, but these only serve to complicate theapparatus. The use of a hot filament as an electron emitter requires aseparate source of heating current and a filament in circuit is alwaysin danger of burning out. In fact, I may say that burnt-out tubes havebeen the biggest plague in radio since the introduction of De Forestsaudion nearly twenty years ago.

According to my present invention, I pro vide a filamentless vacuum tubein which an electronic stream is produced by a photoelectric elementunder the influence of light. A second element in the tube is spacedfrom the photoelectric element, and these two elements are connected ina circuit of substantially constant potential. Between this pair ofspaced elements is interposed a third element adapted to be connected ina circuit of variable electric impulses. This third element acts likethe grid in the old-type tubes in that it controls the electronic flowbetween the two spaced elements in accordance with potential variationsimpressed upon it. The photoelectric element is preferably connected tothe negative side of the circuit, so as to have a negative charge andthus facilitate the emission of electrons. The light for influencing thephotoelectric element is most conveniently derived from an electric lamp1927. Serial No. 199,649.

having constant intensity of illumination. In the basic aspect of myinvention, the source of light rays to which the photoelectric elementis subjected may be outside the vacuum tube or within the tube itself.

- My new tube, having no filament or other form of electrode to beheated, requires no A battery and cannot burn out. It can, therefore, beemployed to great advantage in radio sets, electric phonographs andother amplifying systems, in place of the old filament tubes with onlysuch changes in prior circuits of accepted type as may be foundnecessary for the best results in any particular case.

I shall explain my invention fully and clearly by reference to thediagrams in the accompanying drawings, in which- Fig. 1 shows a vacuumtube constructed in accordance with my invention;

Fig. 2 illustrates an amplifying circuit utilizing my new vacuum tube;

Fig. 3 shows a three-stage amplification system embodying my inventionfor operating loudspeaker mechanism;

Fig. 4 indicatesdiagrammatically an ar rangement whereby three vacuumtubes are operated from a single source of light; and

Fig. 5 shows in plan View an arrangement for controlling the source ofillumination by means of an adjustable shutter.

The vacuum tube T, illustrated more or less diagrammatically in Fig. 1,contains a photoelectric element or body 10, a grid 11 and an anode 12.These three electrodes are 35 rigidly supported in properly spacedrelation in any practical way. For simplicity I have shown thephotoelectric body 10 in the form of a plate supported on stems 13projecting from the base 14 within the tube. The grid 11 is supported bystems 15, and the electrode 12 is mounted in a'stem 16. In order to makeFig. 1 as clear as possible, I have shown the electrodes in diagrammaticform. The element 12 is. represented as a rod or stiif Wire, but it maybe a plate or of any other practical shape or form. A good metal to usefor element 12 is aluminum. The grid 11 may be of the usual constructionfound in radio tubes of the prior art. The photoelectric body isdiagrammatically shown asa flat plate, but it may have any otherpractical shape, such as a wire, grid, button, and the like. In fact,the electrode 10 may simply consist of a deposit of photoelectricmaterial within the tube in such position that when illuminated it willemit a stream of electrons so directed as to be controlled by the grid.The only reason why the plate 10 appears larger than the grid 11 in Fig.1 is to show the presence of element 10 behind element 11. The body 10consists of, or is covered with, wholly or partly, material adapted toemit electrons under the action of light. Among the most activephotoelectric materials, especially when exposed to ultraviolet rays,are rubidium, potassium, sodium, barium, and alloys or amalgamscontaining them.

. element 10 as the cathode and to element 12 as the anode, because thephotoelectric element 10 operates best as an electron-discharging memberwhen impressed with a negative potential. I do not wish to exclude,however, the possibility'of operating the tube by connecting the element10 as. the anode and the element 12 as the cathode. When I speak ofcontainer T as a vacuum tube, both in the description and claims, I meana tube from which the air has been exhausted to the desired degree.

From the base of tube T project four contact pins 17 18, 19 and 20arranged to fit in any standard radio tube socket. The pin 17 isconnected by wire 21 to the photoelectric body 10. The pin 18 isconnected by wire 22 to the controlling grid 11, and pin 19 is connectedby wire 23 to electrode 12. The fourth pin 20 is a dummy and iselectrically inactive.

In Fig. 2 I have shown a simple circuit containing my new photoelectrictube. One side of an input coil 24 leads to the grid 11, and

. the other side of the coil is connected to the anode 12, which isconnected to the positive pole of battery 25, or any other suitablesource of substantially constant potential. The negative side of battery25 is connected to the photoelectric element 10 through an output coil26, which in this instance is shown as the primary of a transformer 27.The secondary coil 28 of the transformer is connected to operate anysuitable mcghanism, such as sound-reproducing apparatus, or any otherdevice adapted to be controlled by variable currents. A source of light29, which is here shown as an electric lamp giving substantiallyconstant light, is arranged to illuminate the photoelectric element 10,as diagrammatically indicated by dotted lines 30. A rheostat 31 ispreferably arranged in the electric light circuit to control the degreeor intensity of illumination of lamp 29. In some instances this lamp maybe operated by battery 25.

If the source of light for cathode 10 is in the tube itself, aspreviously suggested, a glow discharge may be arranged in closeproximity to the cathode.

The'operation of the system shown in Fig. 2 is substantially like this:As long as the photoelectric body remains unilluminated, the batterycircuit is open between electrodes 10 and 12, and therefore no currentflows. When, however, the electrode 10 is subjected to light,particularly ultra-violet rays, a stream of electrons issues fromelement 10, thereby rendering the space between electrodes 10 and 12conductive, so thatcurrent flows through output coil 26. Assuming theinput coil 24 to be traversed by variable electric impulses, which maybe produced by radio reception, operation of a phonograph needle, or inany other way, the variable potential impressed on grid 11 will socontrol the flow of electrons that the current through coil 26 will varyin accordance with, and in greatly amplified relation to, the potentialvariations of grid 11.

The normal electron discharge of cathode 1O depends on the intensity orquantity of illumination furnished by the lamp 29, and

the proper degree or amount of illumination for the best operation ofthe tube can be determined by trial in each. particular case. This lieswell within the experimental skill of the worker familiar with this art.By keeping the illumination of electrode 10 constant, a constant streamof electrons is produced.

Fig. 3 illustrates an amplification system employing three of my newphotoelectric tubes between the input coil 24 and the output coil 26.The secondary coil 28 operates a loudspeaker 32. The anodes 12 of thetubes are connected in parallel to the positive side of battery 25. Oneside of the primary coils 33 and 26 is connected to the negative pole ofthe battery, and the other side of these coils is connected to thecathode 10 of the adjacent tube. The grids 11 of the second and thirdtubes are connected to the secondary coils 34. Otherwise, what has beensaid in connection with Fig. 2'applies to Fig. 3 without the need ofrepetition.

The three tubes of Fig. 3 may be arranged as shown in Fig. 4, so that asingle source of light 35 may illuminate the photoelectric elements 10with the same intensity. The dotted lines 36 represent diagrammaticallythe paths of illumination for the three lamps. If desired or advisable,mirrors 37 and lenses (not shown) may be employed to direct the lightagainst the elements 10. If more than three tubes are used, these alsomay be arranged so that a single lamp will be suflicient to operate allof them.

Instead of controlling the degree or intenin Fig. 2, mechanicalcontrolling means may subject only to mechanical breakage.

the required cient operation of the tube in which it is connected.

be employed. In Fi 5 there is a lamp 38 surrounded by a fixe shield 39and a rotary cylindrical shutter 40. Or, the member 39 may be rotary'andthe member 40 fixed. The shield 39 has windows 41, and the shutter 40has correspondingly arranged windows 42. By adjusting the shutter 40 (or39) the amount of light reaching the photoelectric element of the lampor lamps may be regulated as required. In Fig. 5 it has been assumedthat the lamp controls three tubes, as in Fi 4. The number of windows inthe cylin rical members 39 and 40 will depend upon the number andarrangement of the lamps to be operated. It is hardly necessary toexplain that the light from lamp 29 or 35 strikes the front face of eachcathode 10. The relative arrangement of the lamp and vacuum tubes inFigs. 2 and 4 is merely diagrammatic. So far as my new amplifying systemis con cerned, any practical form of photoelectric tube may be used.

It will be clear from the preceding description that I have provided avaccum tube having marked advantages over the old type three-electrodetubes. As far as I know, this is the first radio tube adapted to operatecold. There being no filament or other electrode to be heated, it isimpossible for the tube to burn out. Even if the electrodes should beaccidentally connected to the wrong battery terminals, no harm would bedone. Electrically speaking, therefore, the life of of the tube ispractically indefinite, it being Furthermore, the hum or line noises dueto filament circuits are completely eliminated b the use of my coldcathode tube, so that better radio reception is obtained. The electrondischarge of the cold photoelectric element 10 does not depend upon theheating action of an electric current, as in the case of hotfilamenttubes, but depends upon a source of light which may be regulated toproduce electron flow for the most sulfiand the system I claim as myinvention:

1. In a system for amplifying electric impulses, a plurality ofoperatively connected vacuum tubes having each a pair of spacedelectrodes and an interposed grid, one electrode of each pair beingadapted to emit electrons under the action of light, and a single sourceof light so arranged in relation to said vacuum tubes as to illuminatethe photoelectric elements of all tubes with substantially the samedegree of intensity.

2. An electric amplifying system comprising a plurality of vacuum tubes,each tube having a pair of spaced electrodes and an interposed grid, oneelectrode of each pair being adapted to emit electrons under the actionof light, means for connecting each pair of electrodes in a circuit ofsubstantially constant otential, means for connecting the grid of thefirst tube in an input circuit of variable potential, said tubes belngconnected to rovide successive stages of amplification, and a singlesource of light so arranged -1 n relation to said vacuum tubes as toilluminate the photoelectric e ements of all tubes with substantiallyconstant intensity.

3. An electric amplifying system comprising a vacuum tube containing apair of spaced electrodes, one ofsaid electrodes being an anode and theother being a cathode adapted to emit electrons under the action oflight, means for connecting said electrodes in a circuit ofsubstantially constant potential, a'grid interposed between saidelectrodes, an 1nput c011 connected to said anode and said grid, and anoutput coil connected to said anode and cathode, whereby changes in gridpotential correspondingly vary the current flow in said output coil inamplified ratio.

, 4. An electric amplifying system comprising a vacuum tube containing apair of spaced electrodes, one of said electrodes being an anode and theother being a cathode adapted to emit electrons under the action oflight, means for connecting said electrodes in a circuit ofsubstantially constant potential, a grid interposed between saidelectrodes, an input coil connected to said anode and said grid, and anoutput coil connected to said anode and cathode, whereby changes in gridpotential correspondingly vary the current flow in said circuit inamplified ratio, and means for varying the intensity or quantity ofillumination of said light-sensitive electrode in order to control thenormal electronic discharge thereof. I

5. In a photo-electric system, the combination of a plurality of vacuumtubes arranged in a circle, each tube containing a photoelectricelement, and an electric lamp placed substantially at the center of saidcircle for illuminating said elements with practically the same degreeof intensity.

6. In a photo-electric system, the combination of a plurality of vacuumtubes arranged in a circle, each tube containing a photoelectricelement, an electric lamp placed substantially at the center of saidcircle for illuminating said elements with practically the same degreeof intensity, and a rotary cylindrical shutter surrounding said lamp toregulate the amountgf light projected onto said elements.

7. An electric amplifying system comprising a plurality of vacuum tubes,each tube having an anode and a photo-electric cathode, a gridinterposed between said two electrodes in each tube, means forconnecting the anode and cathode of each tube in a circuit ofsubstantially constant potential, each of said circuits including aprimary coil, a secondary coil associated with the primary coil betweeneach pair of tubes, each secondary coil being connected to the anode andgrid of the associated tube, an input coil connected to the anode andgrid of the first tube, an output circuit associated with the last tube,and means for simultaneously illuminating all of said photo-electriccathodes with substans tially constant intensity.

8. In a photo-electric system, the combination of a single source oflight, and a plurality of photo-electric tubes grouped about said sourceof light in such a way that the lightsensitive elements of said tubesare simultaneously illuminated with practically the same intensity.

9. A radio receiver system having a plurality of vacuum tubes connectedto provide successive stages of amplification, each tube having a pairof spaced electrodes and an interposed grid, one electrode of each pairbeing adapted to emit electrons under the action of light, and means forsimultaneously illuminating said electrodes with substantialy constantintensity to provide anode circuits which normally are of substantiallyconstant potential.

10. An electric amplifying system, comprising a plurality of vacuumtubes, each tube having an anode and a photo-electric cathode, a gridinterposed between said two electrodes in each tube, means forconnecting said tubes to provide successive stages of amplification, aninput circuit connected to the first tube and an output circuitconnected to the last tube, and means for simult neously illuminatin allof said photo-electric cathodes with su stantially constant intensity.

ADOLPH A. THOMAS.

